The present invention relates generally to the field of electrical power control and more specifically to the field of cycle skipping power control for alternating current (AC) electrical loads.
In a wide variety of applications, power switching devices are used to control the flow of power from an AC line voltage source to an electrical load. Examples of such power switching devices include, but are not limited to, triacs, silicon controlled rectifiers (SCRs), and relays.
Power control strategies for these applications are divided into two categories: phase control, where complete or partial AC line voltage half-cycles are passed to the load; and cycle skipping control, where only complete AC line voltage half-cycles are passed. For many applications, considerations of cost, electromagnetic interference (EMI) generation, low frequency content of the current, and power factor are the basis for selecting which category and which strategy within the selected category is best. In other applications, such as, for example, cooking appliances, additional considerations of cooking element appearance and induced ambient lighting flicker may also be important.
The performance of a particular cycle skipping control strategy depends on the temporal patterns of half-cycles used to realize the various required levels of load current. One design approach pre-stores these temporal patterns. The pre-stored pattern approach is described in Glaser, et al., U.S. Pat. No. 6,246,034 (issued Jun. 12, 2001) and Glaser, et al., U.S. Pat. No. 6,188,208 (issued Feb. 13, 2001).
An alternative design approach generates these temporal patterns in real time. In some cases, a real-time pattern generating system may be implemented in lower cost hardware than a comparable pre-stored pattern system. Opportunities exist, therefore, to reduce the cost of cycle skipping power control systems through the use of real-time pattern generation.
The opportunities described above are addressed, in one embodiment of the present invention, by a cycle skipping power control apparatus comprising: a power controller adapted for receiving a power command and a switch closure feedback signal and for generating a high resolution pulse command; and a pulse generator adapted for receiving the high resolution pulse command and, optionally, the power command, and generating a compensated enable pulse and the switch closure feedback signal.